.outer {
  width: 600px;
  height: 200px;
  margin: 0 auto;
}
.outer .chart-container {
  width: 300px;
  float: left;
  height: 200px;
}
.highcharts-yaxis-grid .highcharts-grid-line {
  display: none;
}

@media (max-width: 600px) {
  .outer {
    width: 100%;
    height: 400px;
  }
  .outer .chart-container {
    width: 300px;
    float: none;
    margin: 0 auto;
  }
}
